That all worked well... So the next step was to pick a FTA DVB-S transponder on the commercial Es'hail satellite and tune the dish up on that as a precursor to accessing the QO-100 Amateur Transponder...

That failed to work and it took a while for the penny to drop as to WHY? But, Hey! this is all a learning curve... But it was so obvious that I should have realised it in the first place !!

Best find another receiver. I think it can be re-programmed. You also need to chose the right FTA signal that's actually receivable in the UK. Better way, align on 28.2 then attach your airspy, if necessary via a suitable downconverter, and look for the transponder while moving the dish a tad to the south.

A good way to line up is the beacon MER on wideband, with no others using the transponder it should be 11-12 dB. For DATV this is what you want optimised and once it is, narrow band will be more than good enough. On Narrow band you need to maximise the beacon amplitude, not the SNR because that dish will see the transponder noise floor well above the background noise and it's hard to tell improvements.